T-lymphocyte activation is regulated by cellular thiols and exogenous factors, including environmental agents that can influence the redox status of the micro-environment of lymphoid organs, which can alter T cell growth, differentiation, and immune function. Infectious diseases can in themselves compromise the redox status of lymphoid cells which may result in additive or synergistic effects on immune effector or accessory cells in the presence of certain environmental agents. The hypothesis to be tested in this application is that environmental agents directly or indirectly dysregulate (suppress or potentiate) immune functions by enhancing oxidative stress in lymphocytes. Modification of cellular thiols alters signal transduction and thiol-dependent enzymes important to lymphocyte activation and proliferation, such as PKC and DNA polymerase alpha and/or delta. This oxidative stress due, in part, to less reduced glutathione (GSH), also modifies specific thiol-reactive consitutents maintaining appropriate plasma membrane (PM) structure/function necessary for appropriate regulation of cell cycle activation events as well as subsequent DNA synthesis and proliferation. Immunomodulation can occur due to the oxidative stress-induced restructuring of PM lipids and proteins (receptors) within lymphocytes and/or antigen-presenting cells. Additionally, the lymphoid subsets especially TH1 and TH2 cells may have differential sensitivities to oxidative stresses which could induce further immune dysregulation. GSH becomes up-regulated during normal T cell activation (which is intrinsically oxidative), and GSH and protein thiols maintain a balanced cellular redox state for proper signal transduction and DNA synthesis. The investigator proposes to confirm and extend the regulatory role of cellular thiols in mitogen-induced DNA synthesis, with emphasis on quantification of cellular thiols, their subcellular distribution and biochemical analyses of signaling events including PM-associated changes which are influenced by the cell's redox state. Total thiols, GSH and surface thiols in lymphoid subsets will be analyzed after in vitro exposure to hydrogen peroxide, g-radiation, thiol-modifying drugs and environmental agents known to have thiol reactivities. The mechanism involved in any impairments (or dysregulation) of activation, growth, differentiation or function (cytokine production) in the various groups will be investigated. The causal involvement of cellular thiols in the inhibition of DNA synthesis by the oxidative stress will be investigated at the cellular, biochemical, and molecular level. Cellular thiol variances between individuals will be correlated to oxidative stress sensitivities with the future goal of risk assessment evaluation.